JPS61218646A - Heat-retaining agricultural film - Google Patents

Abstract

PURPOSE:To produce the titled film having excellent heat-retaining property at night, parallel light transmittance and weather resistance, usable for a long period and disposable easily after use, by compounding a polyolefin resin with a hydrotalcite at a specific ratio and kneading and forming the composition. CONSTITUTION:The objective film can be produced by compounding (A) 100pts. wt. of one or more polyolefin resins selected preferably from low-density PE, linear low-density PE and ethylene-vinyl acetate copolymer with (B) 0.5-40pts. wt. of a hydrotalcite having a refractive index of preferably 1.48-1.52 and kneading and forming the composition.

Description

Detailed Description of the Invention The present invention improves the heat retention properties of agricultural films using polyolefin resin. Specifically, it promotes plant growth by increasing soil temperature during the day and preventing cooling at night, and also has weather resistance. This invention relates to a heat-retaining agricultural film that can be used for a long period of time.

Conventionally, polyvinyl chloride, polyethylene, and ethylene-vinyl acetate copolymers have been used as agricultural films to cover agricultural greenhouses, tunnels, etc. for the purpose of forced cultivation.

However, polyvinyl chloride film has a transmittance of about 15% in the far infrared region of about 5 to 25μ, which is used to prevent heat radiation at night, and although it has an excellent shielding effect, it is difficult to manufacture ultrathin films. Its use is limited due to drawbacks such as difficulty and the fact that the plasticizer contained in the film bleeds onto the film surface during use, making it difficult for dust to adhere to it and significantly impairing the transmission of sunlight. .

On the other hand, films using polyolefin resins such as polyethylene and ethylene-vinyl acetate copolymer can be manufactured into IT films compared to polyvinyl chloride films, and are easier to dispose of as waste after use, making them suitable for agricultural use. In recent years, various uses have been considered for use as film for commercial use.

However, the polyolefin resin film has a significantly inferior shielding effect of 5 to 25 microns in the far infrared region compared to a polyvinyl chloride film, and as a coating film, its heat retention effect at night is extremely poor.

Therefore, a device with an absorption band in the wavelength range of 5 to 25 μ as mentioned above,
Silicic anhydride, silicic anhydride alumina, anhydrous aluminum oxide,
Attempts have been made to add aluminum hydroxide, calcium hydroxide, and phosphate to polyolefin resins, either singly or in combination.

However, agricultural films made from polyolefin resins containing the above-mentioned additives are less transparent than polyvinyl chloride films due to the large difference between the refractive index of the polyolefin resin and the refractive index of the above-mentioned additives. Therefore, the permeability of parallel light rays is poor and the incidence of sunlight is restricted. Moreover, the heat retention at night is only slightly improved.
It is difficult to achieve the same level of heat retention as polyvinyl chloride film, and no satisfactory heat retention film has been obtained.

To solve these problems, attempts have been made in recent years to improve parallel light wA transmittance and heat retention by blending specific polymer compounds such as polyacetal with polyolefin resins. However, in this case as well, the improvement in heat retention is insufficient.

The present inventors have made extensive efforts to solve the above-mentioned drawbacks of agricultural films using polyolefin resins, and to obtain agricultural films that have excellent parallel light transmittance and excellent nighttime heat retention. discovered that by adding hydrotalcites having a refractive index almost equal to that of polyolefin resin, an agricultural film with extremely superior parallel light transmittance and heat retention compared to conventional products could be obtained, and the present invention was developed. completed.

That is, the present invention is a heat-retaining agricultural film made by blending 100 parts by weight of a polyolefin resin with 40 parts by weight of hydrotalcium +- species O, S, and kneading and molding the mixture.

The polyolefin resins used in the present invention include low density polyethylene (d-0,910 to 0.935), high density polyethylene <a = 6.935 to 0.970),
Linear low density polyethylene (d = 0.910~0.93
5), ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, and the like.

Linear low-density polyethylene (LLDPE) is a copolymer of ethylene and other α-olefins, and is made by copolymerizing conventional high-density polyolefins into a short branched structure. Butene, hexene, octene, decene, etc. are used as the olefin. Therefore, polyethylene has a structure that is more linear than conventional low-density polyethylene and more branched than high-density polyethylene.

Among these polyolefin resins, low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymers produce films with superior transparency, flexibility, and weather resistance compared to other resins. Therefore, it is preferable as an agricultural film.

Hydrotalcites used in the present invention (Published by the Gypsum and Lime Society, Gypsum and Lime Disease 187. P47-53 (1983)
) is a hydrous basic carbonate of magnesium and aluminum, and its crystalline properties are two-dimensional, three-sided, or six-sided, and its natural minerals include Mg, ll It z (011)
+ bC (denoted by h・4■20), and is produced in the Snarm region of Norway and the Ural region of the Soviet Union.

Hydrotalcites to be synthesized [published by Ohmsha, Chemical Technology Magazine MOL, February 1972 issue, pp. 31-36] include Kyowa Kagaku Kogyo (Alkamizer I manufactured by +11,
Examples include Alkamizer ■ and DHT-4A.

The refractive index n8 of these hydrocrusites is the refractive index nA = 1.45 of the polyolefin resin used in the present invention.
~1.55, but especially the refractive index n*
If hydrotalcites with = 1.48 to 1.52 are used, the refractive index ratio n a / n B = 0.98 to 1.0
2, and the light transmittance is almost the same as that of an additive-free polyolefin resin film.

It is preferable that the particle size of hydrotalcium II is 5 μm or less because it can be easily dispersed in the resin.

The heat-retaining agricultural film of the present invention obtained in this way does not deteriorate in film strength and weather resistance despite the addition of inorganic substances, and is particularly transparent and has an excellent parallel light L9=M transmittance. In addition to obtaining a film, the heat retention properties at night are greatly improved compared to conventional agricultural films using olefin resins, and are increased to a level comparable to polyvinyl chloride films.

In the present invention, based on 100 parts by weight of olefin resin,
0.5 to 40 parts by weight of hydrotalcites are placed;
In addition, it is preferably 1 to 20 parts by weight. In this case, if the amount of hydrotalcites is less than 0.5 parts by weight, the effect of blocking light in the far infrared region of 5 to 25 μm will decrease, and the heat retention property at night will decrease, which is not preferable.

Further, if the amount exceeds 40 parts by weight, neither heat retention nor weather resistance will improve, and the film strength will decrease, so it is not necessary to add more than 40 parts by weight.

To produce the agricultural film of the present invention, a mixture of polyolefin resin and hydrocrucite at a certain ratio is melt-kneaded using a Pan Bali mixer, roll or extruder, and then subjected to inflation processing and T It is molded into a film using normal molding methods such as die processing.

The film thickness varies depending on the application, for example, 50 to 200μ for greenhouses and tunnels, and 10 to 40μ for multipurpose use.
μ is preferred.

Incidentally, an antioxidant, an antistatic agent, an ultraviolet absorber, etc. may be optionally added as long as they do not impair the properties of the heat-retaining agricultural film of the present invention.

The heat-retaining agricultural film of the present invention can be used for greenhouses, tunnels,
Even when used for various purposes such as mulch, it has a heat retaining property comparable to polyvinyl chloride film, has excellent weather resistance, and is easy to dispose of after use, making it extremely useful as a heat retaining agricultural film.

Example 1 To 75 parts by weight of an ethylene-vinyl acetate copolymer containing 1 ton of vinyl acetate and 15% of old Ml value, true specific gravity of 2.1, refractive index of 1.51,
Hydrocrusites (Mgo, 1
tA10. zs(Oll)z(COs). , I6S.

zll, o, Kyowa Chemical Industry ■Product name Alkamizer 1) 50 parts by weight were blended and melted and kneaded with two heated rolls to produce a mass batch, and 875 parts by weight of ethylene-vinyl acetate copolymer was added to this as a diluent resin. The mixture was melted and kneaded to a thickness of 50 μm using an inflation extruder.
A heat-retaining agricultural film is obtained.

Example 2 The same as Example 1 except that the diluent resin used in Example 1 was changed to low density polyethylene having a density of 0.920.1 value 4.

Example 3 The same as Example 1 except that the diluent resin used in Example 1 was changed to linear low density polyethylene having a density of 0.923.1 value 2.

Example 4 The hydrotalcites used in Example 1 had a true specific gravity of 2.1.
, Mgo with a refractive index of 1.51 and an average particle size of 0.4μ, hJ
j! . , 53(011)z(COz). , 16.・
The procedure was the same as in Example 1, except that 115+1□0 (trade name: Alkamizer ■, manufactured by Kyowa Chemical Industry Co., Ltd.) was used.

Comparative Example 1 This was the same as Example 1 except that the amount of hydrotalcite used in Example 1 was changed to 3 parts by weight.

Comparative Example 2 70 parts by weight of hydrotalcites (Kyowa Chemical Industry special trade name Alcamizer 1) were mixed and kneaded with 100 parts by weight of ethylene-vinyl acetate copolymer having a vinyl acetate content of 15% by weight and an Ml value of 2. An agricultural film with a thickness of 50μ is obtained by using an inflation extruder.

Comparative Example 3 The hydrotalcites used in Example 1 had an average particle size of 3.
The procedure was the same as in Example 1 except that 50 parts by weight of 3μ silicon oxide was used.

As described above, regarding the heat-retaining agricultural films of the present invention obtained in Examples 1 to 4 and the comparative films of Comparative Examples 1 to 3, (A) transparency and (U) heat retention were measured under the following conditions.

(a) Transparency Parallel light transmittance was measured using a haze meter according to the following formula according to JIS K-6714.

Parallel light transmittance - Total light transmittance - Haze value (diffuse light transmittance) (b) Heat retention During November 1982 in Noda City, Chiba For 10 days, the soil temperature under the film coating The average value was calculated.

For comparison, low-density polyethylene and ethylene-vinyl acetate copolymer (EV
A) and (B) were measured for a film using polyvinyl chloride.

Table 1 Transparent table Table 2 Heat retention

Claims (1)

[Claims] 1. A heat-retaining agricultural film prepared by blending 0.5 to 40 parts by weight of a hydrotalcite with 100 parts by weight of a polyolefin resin and kneading and molding the mixture. 2. The refractive index of hydrotalcites is 1.48 to 1.5
2. The heat-retaining agricultural film according to claim 1, which is 3. The heat-retaining agricultural film according to claim 1, wherein the polyolefin resin is one or more of low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer.